Converter for continuous acid-saccharification of starch



'May 27, 1969 YOSHIAKI mm. ET AL 3,446,664

CONVERTER FOR CONTINUOUS ACID-SACCHARIFICATIQN OF STARCH Filed Sept. 28, 1965 Sheet ofS May 27,1969

YOSHIAKI KOMAI ET AL CONVERTER FOR CONTINUOUS ACID-SACCHARIFICATIONQF STARCH Filed Sept. 28, 1965 ga a IIIII'IIIIIII I g I 'IlIIllIIllIIIIl'IIllI,/

Sheet 2 01-3 D E J Swap Tima v mi1\ y 7, 1969 YOSHlAKl KOMAI ET AL CONVERTER FOR CONTINUOUS ACID-SACCHARIFICATION OF STARCH Filed Sept. 28,1965

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Sheet 3 United States Patent US. Cl. 127-28 1 Claim ABSTRACT OF THE DISCLOSURE A converter for continuous acid-saccharification of starch. A vertical multi-tube heat exchanger is connected to a plurality of parallel and vertical reaction tubes by three-way cocks and connecting pipes for easily altering the routing of the flow through said reaction tubes. A plurality of groups of rectifying plates, each having a plurality of small orifices, are positioned in said reaction tubes with a group at both ends thereof. A teardropshaped rod extends through the center of each plate in a group and supports the plates spaced from each other. The heat exchanger consists of a central steam heating pipe, a cylindrical wall around said central pipe and defining an annular heating chamber around said central pipe, a steam jacket surrounding said cylindrical wall, a plurality of small cross section steam tubes in said annular heating chamber and extending along the length thereof and offering minimum friction to flow through said chamher. The ends of said steam tubes open through said cylindrical wall into said steam jacket.

The present invention relates to a converter for continuous acid-saccharification of starch. More particularly, the invention relates to a converter for continuous acidsaccharification of starch, comprising a metering or dosing pump adapted to continuously feed a starch slurry prepared to a predetermined starch concentration and acidity, a multitubular heat-exchanger connected with said pump and adapted to heat said slurry under elevated pressure and at a temperature above 100 C., a plurality of reaction tubes of comparatively large diameter and small length and connected to said heat-exchanger, said reaction tubes being installed in vertical arrangement so as to impart a uniform current to the reaction mixture with the progress of saccharification, yielding hydrolysates of superior quality as a result of the consequent identical rate of flow of molecules in the converter.

The object of the invention is to provide a converter for continuous acid-saccharification of starch, capable of producing starch hydrolysates of superior quality.

The outstanding features and advantages of the converter of the present invention include:

l) The heat-exchanger and reaction tubes are installed in vertical and parallel arrangement. I

(2) The heat-exchanger is a compactly-built heat-exchanger of the multitubular type, adapted to give a large heating area per unit length and, accordingly, effectively heat the starch slurry.

(3) The plurality of reaction tubes are vertically installed so as to minimize the surface resistance with respect to the flow as compared with the conventional continuous saccharification tube.

(4) There are provided perforated plates or elements at both ends of each reaction tube so as to ensure a uniform flow rate within the tube (FIG. 3); and

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(5) The provision of three-way cocks connected to respective pipes and reaction tubes makes for a variable flow distance through the reaction tubes (FIG. 1).

No commercial plant utilizing vertical saccharification tubes has ever been reported.

Thus, the renowned Kryziyers (1) plant for continuous saccharification of starch comprises an inclined heatexchanger and a plurality of straight reaction tubes horizontally arranged and connected with each other through U-bends.

Kingma (2) has etfected some improvement in his saccharification system with respect to the liquefaction of starch at the early stage of reaction by automatically circulating a predetermined proportion of the liquefied product bypassed from the primary heater for the purpose of diluting or lowering the high viscosity of starch in the initial reaction period. However, in other aspects than those mentioned of Kingmas converter, no particular diiference is found between this and Kroyers converter.

In the United States (3), the acid-saccharification of starch has generally been carried out by direct heating with steam in order to liquefy the starch slurry and, at the same time, to heat the slurry to a temperature as high as necessary for the reaction. In this instance, there also are provided a plurality of reaction tubes of some great length installed in horizontal arrangement and successively interconnected through U-bends.

A unique design has been offered by Mautner (4), who has employed a conical bowl capable of running at a high speed as a high-performance heat-exchanger for the purpose of liquefying a starch slurry and provided plate heaters in the way of principal reaction chambers.

It is now apparent that whereas other diverse chemical plants have been primarily constructed in vertical arrangement, it seems to have been considered impossible or impracticable to install a starch-saccharification plant in vertical arrangement. We have found, however, that it is not fruitless to construct a vertical plant for acid conversion as might have been suggested, but actually a vertical installation of the plant has a number of advantages.

The present invention is based on this finding and, as such comprises a vertical-heat exchanger and a plurality of vertical reaction tubes.

The present invention will hereinafter be described in detail, reference being had to the accompanying drawings, in which:

FIG. 1 is a schematic diagram showing the arrangement of a continuous starch-saccharification plant embodying the principles of the present invention.

FIG. 2 is a sectional view, on an enlarged scale, of one of the reaction tubes of the invention, showing the perforated disks or plates installed therein.

FIG. 3 is a sectional view, on an enlarged scale, of the conventional reaction tube.

FIG. 4 is a graphic representation of the composition of corn syrup according to Corn Industrial Research Foundation (5), (6).

FIG. 5 is a graphic representation of the composition of the corn syrup prepared according to the invention on a commercial basis.

FIG. 6 is a graph showing the typical D.E. increases with the progress of acid-saccharification of corn starch according to the invention under various conditions.

FIG. 7 is a graph showing the relationship between the acid-to-starch ratio and the degrees of hydrolysis reached after a 20-minute reaction at three different temperatures.

FIG. 8 is a front view, in partial section, of the heatexchanger of the invention; and

FIG. 9 is a cross-section view taken on the line 11-11 of FIG. 8.

Referring, now, to FIGS. 8 and 9, a heat-exchanger 17 is of the multitubular construction, comprising a steam jacket 1, a cylindrical wall 2, a steam chamber 10, a central steam-heating pipe 3, a heating chamber 4, a group 6 of tubes of small diameter arranged inside said reaction chamber 4. The group of tubes 6 open, at their bent ends, through the cylindrical wall 2 so that the steam admitted from a valve 12 is caused by baffles 7, to flow, for the most part, down the tubes 6, thereby preventing much of the steam from flowing down the jacket. Steam from pipes 6 flows out through outlet 38. The heating of the chamber 10 is effected by the steam admitted through a valve 39 and which flows out through outlet 38, and in addition steam is admitted through valve 11 to the central pipe 3 which also is usable for heating purposes. Pipe 3 has outlet 41 at the lower end thereof.

Indicated with numerals 8 and 9, respectively, are an inlet and an outlet for the heating chamber 4. The cylindrical jacket 1 is provided with inert-gas vent valves (not shown) at its upper portion and with heat exchange medium jackets 45 and 40 around the upper and lower ends thereof, having heat exchange medium inlets and outlets 43, 44, 50 and 51. The heat-exchanger of the present invention consists of several components which may be easily assembled and disassembled. The small diameter tubes 5 disposed within the heating chamber 4 are usually connected in parallel with the centerline of the heat-exchanger, although they may be installed at a slight angle with said centerline.

It is preferable to employ twisted tubes instead of straight tubes. This is because tubes, if twisted with respect to the cylindrical wall 2 and central pipe 3 will not only give somewhat greater surface area in the heatexchanger but also give a much improved thermal efficiency since the tubes are at angles with the direction of flow. The described system for heating a viscous slurry is capable of accomplishing an effective stirring of a syrupy material to attain a uniform temperature distribution, which in turn, gives a uniform viscosity distribution at various points of flow due to the identical progress of heat energy uptake and consequently an identical reaction rate of various molecules.

In a tank 13, a starch slurry of the desired starch concentration and acidity is prepared. A metering pump 14 continuously feeds the starch slurry to the converter, and there also are provided a pressure gauge 15 and a safety valve 16. The starch slurry to which acid has been previously added enters, under pressure, into the heat-exchanger 17 through its lower end and emerges, also under pressure, from the upper end of the heatexchanger. The reaction mixture then flows through vertical reacation tubes 18, 19 and 20 which are successively connected, in that order, with said heat-exchanger 17, and further through a discharge valve 21 into a flash tank 22.

Indicated with numeral 23 is a pressure gauge that indicates the terminal pressure within the reaction tube, 24 is a thermometer, 25, 26, 27 and 28 are three-way switch cocks, and 29 and are connecting tubes.

The overall heat transfer coefficient of the heat-exchanger of this invention is U=400 Kcal/m. /cm./hr. when the tubes are made of stainless-steel and a corn starch slurry of Be 22 is saccharified with oxalic acid at 145-l55 C. In case copper tubes are used instead of said stainless-steel tubes 5, the overall heat transfer coeflicient is U=430 Kcal/ m. cm./ hr.

While the performance of the heat-exchanger must be such as to give an efficient turbulent flow and a large heating surface area in a limited space for rapid heating of the viscous liquid into a homogeneous phase, the reaction tubes 18, 19 and 20 must prevent the dissipation of heat owing to radiation not only to ensure a rapid progress of the reaction, but also to prevent the occurence of a heterogeneous phase (in respect of the 4 viscosity and density) due to cooling across the tube Walls.

The maintenance of an uniform flow in the reaction tubes is of the utmost importance for effective hydrolysis of starch molecules in order to attain hydrolysates 0f comparatively analogous composition. In this connection, the utilization of long horizontal tubes of small diameter is not desirable for attaining an uniform flow rate across given sections of the tubes. The wall effect on the flow due to the friction between the surface and fluid is less pronounced with smaller surface areas. It is, therefore, natural to assume that reaction tubes of circular section, large diameter, and small length are suited to the purpose of maintaining an ideal flow.

In addition, the upward flow system of the equipment of this sort could more or less cancel out the reaction temperature drops due to cooling and the consequent reduced flow rate near the wall surface.

And this consideration is of some importance in the design of a converter of the continuous reaction system. This is especially so at early stages of hydrolysis because of the high viscosity of the polymer paste. However, the disadvantage encountered by the designer of a vertical plant is that, with a tube of small length-to-diameter ratio, a slight turbulent flow could have a multiplied influence on the uniform passage and progress of reaction of the molecules in the product. Therefore, in designing reaction tubes, it is preferable to select the proper length-to-diameter ratio.

The total flow of the reaction mixture within the converter of this invention is divided into about 20% for the heat-exchanger and about for the reaction tube. The reaction tube is so designed, in respect its diameter, that the velocity of the reaction mixture is only l-3 cm./sec.

For all practical purpose, however, it is of convenience to install two or three length (19, 18, and 20 in FIG. 1) of a tube and join the length with three-way cocks. In this manner, the flow distance may be widely varied to reduce the reaction time by a substantial amount.

Thus, in order to produce hydrolysates of wide D.E. (degree of hydrolysis) range, the following routing of the reaction tube system may be utilized.

(1) Reaction tube 18+Valve 25+Valve 26+Valve 27+Valve 28+ Discharge valve 21+ Flash tank 22, shown in FIG. 1 with a right vertical section deleted.

(2) Reaction tube 18+Valve 25+ Connecting pipe 29+Valve 31+Reaction tube 19+Valve 26+Valve 27+ Valve 28+ Discharge valve 21+Flash tank 22.

(3) Reaction tube 18+Valve 25+Connecting pipe 29+Valve 31+Reaction tube 19+Valve 26+Valve 27+ Connecting pipe 30+Valve 32+Reaction tube 20+Valve 28+ Discharge valve 21+Flash tank 22.

(4) Reaction tube 18+Valve 25+Valve 26+Reaction tube 19+Valve 31+Valve 32+Reaction tube 20+Valve 28+ Discharge valve 21+ Flash tank 22.

(5) Reaction tube 18+Valve 25+Valve 26+Valve 27+ Connecting pipe 30+Valve 32+Reaction tube 20+ Valve 28+Discharge valve 21+ Flash tank 22.

(6) Reaction tube 18+Valve 25+ Connecting pipe 29+Valve 31+Valve 32+ Reaction tube 20 Valve 28+ Discharge valve 21+ Flash tank 22.

Of course, the reaction velocity may be controlled by varying the reaction conditions, such as the concentration and pH of the starch slurry and the reaction temperature.

Another variable is the period of time during which a given temperature is maintained under a set of conditions within the converter.

In this manner, a far wider choice may be had than is the case with the conventional system.

However, a problem remains to be solved even with the present system, that is, in respect of the connection between the reaction tube and the cock. The problem is concerned with the reaction mixture gushing into the bottom of the tube at a high velocity (40-60 cm./ sec.) through the connecting pipe.

In order to minimize the violent turbulent flow at the end of the reaction tube, it is essential to modify or convert the rapid flow to an uniform flow. For this purpose, perforated plates or wire-mesh screens are used (see FIG. 2). These plates or screens (hereinafter referred to sometimes as rectifying plates) 33, 34 and 35 may be positioned inside flange at a spacing of 2-5 cm. The rectifying plates have openings of varied diameters or different space ratios with respect to the total area and fitted stepwise as above in the order of lower to higher space ratios. When these rectifying plates are installed with a pear or teardrop-shaped rod 37 running through the center of each other plate and locked into position between flanges of the tube, the high-speed current entering from a pipe 36 is gradually converted to a slow uniform flow as it is obstructed by the rod 37 and rectifying plates.

What merits attention is the fact that the rectifying effect is more pronounced on a highly viscous fluid than on a less viscous fluid and that the flow resistance is greater when the contact area of the tube is greater.

FIG. 6 shows the typical D.E. increases with the progress of reaction when corn starch is saccharified under various conditions in the converter of the present invention.

FIG. 7 shows the relationship between the degree of hydrolysis reached after 20 minutes of reaction and the oxalic acid-to-starch ratio at three different temperatures. These date have been obtained from an experiment with a pilot plant, the only tangible difference from a fully industrial plant has been its somewhat inadequate heat insulation. Thus, actual data would show a slightly greater saccharification.

FIG. 5 shows the changes in composition distribution of dextrose and oligosaccharides with the progress of the present converter using 0.35% of oxalic acid (relative to dry starch) at the temperature of 150 C., with comparable C.I.R.F. data (5) (6) being shown in FIG. 4.

Taking analytic errors into consideration, the minor differences between the two sets of data (FIGS. 4 and 5) are negligible. It will now be apparent from the above description that the converter of the present invention is quite superior to any converter of the conventional type.

Literature cited:

(1) K. Kryerz (1955).

(2) W. G. Kingma: Die Starke 9, 189 (1957).

(3) R. H. Rogge: Ind. Eng. Chem., 41, 2070 (1949).

(4) E. Mautner: Die Starke 11, 234 (1959).

(5) W. W. Moyor, S. M. Cantor: Report to Corn Industrie Research Foundation (1941).

(6) B. L. Scallet: Die St'zirke 14,7 (1962).

What we claim as our invention:

1. A converter for continuous acid-saccharification of starch, comprising a vertical multi-tube heat exchanger, a plurality of parallel and vertical reaction tubes, three- Way cocks and connecting pipes interconnecting said reaction tubes with each other and with said heat exchanger for easily altering the routing of the flow through said reaction tubes, a plurality of groups of rectifying plates each having a plurality of small orifices and positioned in said reaction tubes with a group at both ends thereof, a teardrop-shaped rod extending through the center of each plate in a group and supporting the plates spaced from each other, said heat exchanger consisting of a central steam heating pipe, a cylindrical wall around said central pipe and defining an annular heating chamber around said central pipe, a steam jacket surrounding said cylindrical wall, a plurality of small cross section steam tubes in said annular heating chamber and extending along the length thereof and offering minimum friction to flow through said chamber, the ends of said steam tubes opening through said cylindrical wall into said steam jacket.

References Cited UNITED STATES PATENTS Die Sta'rke 6, 119 (1954); 7, 257

2,337,688 12/1943 Sipyaguin et a1. 127-28 X 2,359,763 10/1944 Horesi 127-38 2,735,792 2/1956 Kryziyer 127-28 X 3,236,687 2/1966 Smith et a1 127-38 MORRIS O. WOLK, Primary' Examiner. SIDNEY MARANTZ, Assistant Examiner.

US. Cl. X.R. 127-1, 36, 38; -157 

